Attraction−Repulsion Mechanism for Carbon Monoxide Adsorption on Platinum and Platinum−Ruthenium Alloys

Abstract

Cluster and periodic density functional theory (DFT) of carbon monoxide adsorbed atop on Pt (COads) show that ruthenium alloying weakens both the COads internal and C−Pt bonds and reduces the COads adsorption energy. A new theoretical model based on the π-attraction σ-repulsion is used to explain the above results. This model correlates (1) Mulliken population, (2) density-of-states analysis of the COads orbitals, (3) the individual interaction of these orbitals with the metal lattice bands, and (4) their polarizations within the COads molecule. In this study, the σ interaction has both attractive and repulsive components via electron donation to the metal bands and Pauli repulsion, respectively. Cluster DFT shows that the overall weakening of the COads internal bond upon alloying is due to the dominance of reduced σ donation to the metal (which weakens the COads internal bond) over increased π bonding between the carbon and oxygen. However, periodic DFT calculations show that both the σ donation and the COads internal π bonding are simultaneously reduced. The C−Pt bond weakening upon alloying is primarily due to increased exchange repulsion between the adsorbate and the substrate. The adsorbing Pt atom sp/d z 2 orbitals population increase upon alloying for both calculations.

Controlling the Adsorption of Carbon Monoxide on Platinum Clusters by Dopant‐Induced Electronic Structure Modification

“…[3] Thei nteraction of transition-metal surfaces with CO is ac omplex problem which has been described by three qualitative models:the d-band center model, [8] the Blyholder model, [9] and the p-s model. [10] In the Blyholder model, the Pt-CO interaction is described by donation of electron density from the CO 5s orbital to the empty Pt 5d states and back-donation from occupied Pt 5d states to the CO 2p*antibonding orbital. Theb ottom line of local electronic structure modifications as explanation for the CO tolerance in Pt-X alloy nanoparticles is that electron transfer from the alloying agent to the empty Pt 5d states reduces the Pt-CO bonding strength.…”

Electron density topological and adsorbate orbital analyses of water and carbon monoxide co-adsorption on platinum

“…3d), the absence of correlation between the C-Metal stretching frequency and the corresponding Eads has been reported (Ref. 14,17,89). The C-Metal stretching frequency and Eads are derived from local and global properties of the potential energy surface, respectively: The C-Metal stretching frequency is more closely associated with localized interactions of the adsorbate with the metal atom, whereas the Eads is associated with interactions between the adsorbate and the entire substrate surface.…”

“…24 In the extended π-σ model, the effect of the 5 orbital on the internal COads bond is small. 14 The extended π-σ model has been used by other research groups. [25][26][27][28] We described an expression that correlates changes in to changes in the COads, C and O atomic orbital charges (Ref.…”

Effects of Charge Transfer on the Adsorption of CO on Small Molybdenum‐Doped Platinum Clusters

“…[4][5][6] Diverse models have been suggested to describe the atop bonding mechanism between CO and Pt. Of the most used are the Blyholder model, [7] its more quantitative refinement the π-σ model, [8] and the d-band center model. [9,10] In the Blyholder model bonding is attributed to electron transfer from the occupied 5σ molecular orbital (MO) of CO to the empty Pt d-states and back-donation of electrons from occupied Pt dstates to the CO 2π* MO, which is unoccupied in the free CO molecule.…”